The use of code division multiple access (CDMA) is being proposed for the next generation of cellular telecommunication networks. Additionally, code division multiple access is also being used in the IS-95 Standard in the USA. CDMA is a direct sequence spread spectrum technique. In a wireless cellular network using CDMA, the mobile terminals in one cell associated with a first base station will use the same frequency as mobile stations in an adjacent cell associated with a second base station. The different mobile stations can be distinguished by the respective base stations as each mobile station will be using a different spreading code.
In the proposals for the wideband CDMA standard, it has been proposed that a mobile station or other user equipment in a RACH (random access channel)/FACH (forward access channel) state use the uplink RACH channel to transmit data or messages to a base station and listen to the downlink FACH for data or messages from the base station. In the RACH/FACH there is little or not data being transmitted between the mobile station and the base station such that no dedicated channels have been set up therebetween. The FACH and RACH channels are both common channels which means that all the user equipment including mobile stations in a cell associated with a given base station will use these channels.
The data is sent in data frames. Data frames sent from the base station to the mobile stations will include the identity of the user equipment, for example the identity of a mobile station. Each mobile station will receive all the data frames sent from a base station to the mobile station on the FACH. Each mobile station is able to identify the data frame intended for that mobile station by the identity included in the frame. The frames sent from the mobile station include information identifying the source of the frames.
As a number of mobile stations or user equipment share the FACH channel it is difficult to set the power level of that channel such that it is at the lowest possible level and at a level such that all the mobile stations can receive the signals from the base station. In CDMA systems, the number of users which can be supported by the system with a given quality of service depends on the total signal power of all the users and the base station in a cell. If the total signal power is relatively high, this will provide a relatively high level of interference. This means that it may be difficult to distinguish the desired signal from the interference resulting from the other base stations. Accordingly minimisation of the power used by each user and the base station will improve the capacity and/or quality of service.
EP-A-0-892572 describes a BCCH carrier supporting a physical BCCH such that at least one BCCH timeslot is entirely received within one of the successive monitoring windows of a mobile station of an adjoining cell.